Sled-Type Motion on the Nanometer Scale: Determination of Dissipation and Cohesive Energies of C 60

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Abstract
The tribological properties of C60 on the mesoscopic scale were investigated with a scanning force microscope, which allowed simultaneous measurements of normal and lateral forces under ultrahigh-vacuum conditions. Islands of C60, deposited on NaCl(001), could be moved by the action of the probing tip in a controlled way. Different modes of motion, such as translation and rotation, were observed. An extremely small dissipation energy of about 0.25 millielectron volt per molecule and a cohesive energy of 1.5 electron volts were determined in these nanometer-scale experiments. The corresponding shear strength of 0.05 to 0.1 megapascal was smaller by one order of magnitude than typical values of boundary lubricants. For C60 on graphite, disruption of the islands was observed and collective motion of the islands could not be achieved. These results could find use in the field of nanotechnology; for example, C60 islands could be developed into a sled-type transport system on the nanometer scale.